This invention relates to hydrocarbon-resistant sealants and in particular to hydrocarbon-resistant sealants having acceptable craftability and seal reliability characteristics even when formulated with fire-retardant materials for flame resistance.
The sealants of the present invention are particularly useful for cable splice closures that provide a protective barrier for sealing closures, splice cases or other outside telecommunications apparatus from damage caused by environmental exposure. Historically, cable splice closure sealants were based upon butyl rubber. However, such sealants soften and do not perform well in hydrocarbon contaminated environments commonly found in manholes. Butyl rubber based sealants also fail to meet the flammability standards of new fire resistance requirements for building closures.
In addition to hydrocarbon and flame resistance, cable splice closure sealants must be sufficiently pliable to form a seal during installation. This characteristic is defined as craftability. Once formed, the sealant must maintain seal integrity by adhering to hard substrates such as metal, rubber or plastic across temperature extremes that not only soften or harden the sealant but also subject the seal to stress from the expansion and contraction of the seal assembly. The seal assembly is also subjected to the air pressure to which the cable system is internally pressurized, typically up to 10 psi. The characteristic ability to withstand such environments is known as seal reliability.
Levy et al., Intern. Wire & Cable Symp.Proc. 1986, 289-298, discloses the use of oil-resistant rubber to formulate hydrocarbon-resistant sealants. This article discloses that it is not possible with the polymer used to develop a single formulation that is both hydrocarbon and flame resistant and possesses the necessary craftability and seal reliability characteristics. Instead, separate hydrocarbon-resistant and flame-resistant compositions are disclosed. The sealants disclosed possess marginal craftability and seal reliability.
A hydrocarbon-resistant sealant with improved craftability and seal reliability would be highly desirable. It would be even more desirable if such a hydrocarbon-resistant sealant could be made flame resistant by formulation with fire-retardant materials and maintain an acceptable level of craftability and seal reliability.